Environmental Changes Harming Lake Life Up North, Researchers Say

A water flea, Daphnia magna

Public domain image by Upper Midwest Environmental Sciences Center, U.S. Geological Survey, U.S. Department of the Interior

Acid rain and other environmental changes have caused calcium declines in Canadian Shield lakes, taking a toll on tiny crustaceans called Daphnia, researchers report in the 27 November issue of Science.

These organisms, also known as water fleas, are important algae grazers and prey for small fish, so their decline may signal larger ecological disruptions in the freshwater food-webs in eastern Canada and possibly other parts of the northern hemisphere.

Daphnia depend on calcium in the lakewater, but the calcium levels have been declining, as the result of both natural processes and human-related changes including acid rain and logging.

"Calcium is required by all organisms. We call [calcium declines] colloquially 'aquatic osteoporosis,'" said John Smol of Queens University, who is a coauthor of the Science study.

To investigate how the calcium declines were affecting lake life, Adam Jeziorski of Queen's University and colleagues analyzed sediment cores and water chemistry data from a variety of Canadian lakes. They found that Daphnia populations had become depleted in recent decades—in some cases nearly disappearing—in patterns that corresponded to the lakes' calcium declines.

"This is all very worrisome," said Smol. "The good news is that we have found the 'miner's canary' in the form of these water fleas that track the decline in calcium levels. The bad news is that many lakes have already passed these critical thresholds."

Kathleen Wren

1 December 2008